1. Field of the Invention
The invention relates to a wrench, more particularly to an electronic torque wrench.
2. Description of the Related Art
Referring to FIG. 1, a conventional electronic torque wrench, as disclosed in U.S. Pat. No. 4,958,541, includes a ratchet head 1, a deflection beam 2 connected to the ratchet head 1, a plurality of strain gauges 3 fixed to the deflection beam 2, a handle 4 connected to the deflection beam 2, a circuit board 5 disposed within the handle 4 and connected electrically to the strain gauges 3, a tactile indication generator 6 disposed within the handle 4 and connected electrically to the circuit board 5, and a battery 7 disposed within the handle 4 and connected electrically to the circuit board 5 and the indication generator 6. The indication generator 6 has an electric motor 601, and a mass 602 fixed eccentrically to a shaft of the motor 601.
When a user rotates a workpiece (not shown) using the conventional electronic torque wrench, the strain gauges 3 transmit a detected torque to the circuit board 5. If the torque is greater than a reference torque level, the circuit board 5 actuates the motor 601 to rotate the mass 602. Since the mass 602 is eccentrically mounted on the motor 601, it will tend to vibrate the motor 601 as it rotates. The vibration is transmitted to the handle 4, thereby warning the user to stop the operation.
Although the aforementioned conventional electronic torque wrench can achieve its intended purpose, it has the following drawbacks:
Since different users have different sensitivities with respect to the vibration, and since the user may slightly loosen his hold on the handle 4 when the vibration occurs, the user may not feel the vibration, and thus miss the warning.